This disclosure relates generally to brake pressure proportioning in-line ball valves, and more particularly to an improved valve having relatively few components and a relatively short length.
Brake proportioning valves are used in automobiles and other vehicles. In these applications, it is often necessary to proportion brake fluid pressure between front and rear wheel brakes, or cylinders, as less braking power is needed in the rear wheel brakes. A brake pedal is operably attached to a master cylinder, which is connected to the wheel brakes via hydraulic lines. Depressing the brake pedal causes the master cylinder to increase hydraulic pressure at its outlet. The master cylinder outlet is connected to separate hydraulic lines for the front and rear wheel brakes, or for the right and left wheel brakes, to carry the increased hydraulic pressure through the lines to the respective wheel brakes. In either case, a brake proportioning valve, or a plurality of brake proportioning valves, is disposed between the master cylinder outlet and the rear wheel brakes to allow proportionately less hydraulic pressure from the master cylinder to reach the rear wheel brakes, thereby achieving the proper braking proportion.
The brake proportioning valve has an inlet connected to the master cylinder, and an outlet operably connected to the rear wheel brakes. At low inlet pressures, where the brake is not applied, brake fluid flows freely in both directions through the brake proportioning valve. However, as brake fluid pressure increases at the valve's inlet in response to application of the brake pedal, a predetermined level is reached where pressure at the valve's outlet forces a piston to engage a ball to restrict the flow of brake fluid to the rear wheel brakes.
This predetermined level is known as the knee point pressure, and is equivalent to the force holding the valve open divided by a differential relating to the area of the inlet pressure seal and the area of the outlet pressure seal. For the valve to perform, the outlet seal diameter must be greater than the inlet seal diameter. Thus, there is a benefit in making the inlet seal diameter as small as possible so that the outlet seal, and therefore the entire valve, does not take up a great deal of space.
A brake proportioning valve of the prior art is disclosed in U.S. Pat. No. 5,522,651, and provides proportioning of brake fluid pressure using a plunger of two diameters against which hydraulic pressure operates, and a check ball located in the plunger and held off its seat under low outlet pressure conditions by a rod and valve lifter. The ball is biased in place by a ball spring. At high outlet pressure, i.e., above the knee point pressure, the plunger contacts the ball and restricts fluid flow. A continuation-in-part of the above-referenced patent, U.S. Pat. No. 5,741,049, operates similarly.
However, several disadvantages are associated with this prior art. First, the rods do not directly engage their respective housings. Instead, each rod requires extra elements, such as a valve lifter assembly, to support the rod, thereby complicating manufacture. Second, the ball springs could become completely compressed by the balls, undesirably restricting fluid flow. Third, the outlet seal diameters are larger than their respective plunger springs' diameter, thus limiting the variety of plunger spring strengths that can be used, and hence lowering the possible range of knee points.
Therefore, what is needed is an apparatus having less components and steps in assembly, as well as a shorter length when compared to the above system, without having the disadvantages associated with the systems.